NVIDIA HB SLI Bridge: A Technical Review
Along with the latest GeForce GTX 1080 graphics card, we were introduced to the new NVIDIA HB SLI Bridge. In this article we have a closer look at the internals of the new SLI bridge.
NVIDIA HB SLI Bridge Introduction
In the past, graphics cards powered by an NVIDIA GPU sporting one Scalable Link Interface (“SLI”) connector supported only 2-Way SLI. Graphics cards with two SLI connectors supported 3-Way and 4-Way SLI. The majority of SLI systems use two graphics card in 2-Way SLI configuration, so NVIDIA decided to combine both connectors to improve the communication between the graphics card’s GPUs by increasing the bandwidth. The new bridge is called High Bandwidth (“HB”) bridge.
The SLI connector itself is mainly for communication between the master and the slave card(s). There are several different SLI modes such as AFR or SFR and the cards have to communicate with each other to coordinate the frame rendering. NVIDIA has brief documentation available on the various SLI configuration methods on their website, however there is little public information available on the specific data that is transferred over the bridge. Considering that NVIDIA has supported SLI communication over the PCIe interface, allowing SLI without the need for a bridge, it’s not unreasonable to assume SLI doesn’t require a high bandwidth bridge to operate.
Apart from the performance scaling, micro-stuttering is one of the biggest problems of SLI. According to NVIDIA the increased bandwidth of the new SLI bridge should also help to improve the SLI experience by reducing the micro-stuttering.
Legacy SLI bridges operate at a frequency of 400 MHz and only use one SLI finger (connector). The NVIDIA HB SLI Bridge can operate at 650 MHz and use both SLI fingers which should increase the bandwidth in theory and also allow a faster communication between both cards.
NVIDIA recommends to use either the LED or HB SLI Bridge for any operation above 1080p resolution. The LED bridges launched back 2014, which begs the question: what’s all the fuss about? Apart from using both SLI connections, what makes the HB Bridge special?
Reading reviews on several other websites you can see that there is either a) no difference at all, b) a very small difference or c) suddenly a huge performance increase in some specific applications or games.
So I decided to do my own performance testing. Along with studying the effect on performance, I also wanted to find out more about the electrical and physical differences between the various SLI bridges. I sent a couple of different SLI bridges to a special lab for X-ray analysis. The X-ray analysis shows traces inside the PCB which you usually can’t see and also indicates the quality of the solder connections.
(PSA: X-ray analysis is not cheap. If you feel my content is worthwhile and you want to support me, check out the affiliate links below)
Available NVIDIA SLI BridgesBelow a list of available NVIDIA SLI bridges
|ASUS||Republic of Gamers Flexible 2-Way SLI Bridge||Flexible||2-Way||40mm||Link|
|ASUS||SLI Flexible Bridge||Flexible||2-Way||70mm||Link|
|ASUS||SLI Flexible Bridge||Flexible||2-Way||120mm||Link|
|ASUS||3-Way SLI Flexible Bridge||Flexible||3-Way||Link|
|Tekit||SLI Flexible Bridge||Flexible||2-Way||150mm||Link|
|EVGA||PRO SLI Bridge HB||HB||2-Way||40mm||Link|
|EVGA||PRO SLI Bridge HB||HB||2-Way||120mm||Link|
|NVIDIA||GeForce GTX SLI HB Bridge 3-Slot||HB||2-Way||60mm||Link|
|NVIDIA||HB SLI Bridge 4-slot||HB||2-Way||120mm||Link|
|ASUS||ROG Enthusiast 2-Way SLI Bridge||Solid||2-Way||40mm||Link|
|ASUS||ROG Enthusiast 3-Way SLI Bridge||Solid||3-Way||Link|
|ASUS||Nvidia 3-Way SLI Bridge||Solid||3-Way||Link|
|ASUS||ROG Enthusiast 4-way SLI Bridge||Solid||4-Way||Link|
|EVGA||Pro SLI Bridge V2||Solid||2-Way||40mm||Link|
|EVGA||Pro SLI Bridge V2||Solid||2-Way||60mm||Link|
|EVGA||Pro SLI Bridge V2||Solid||3-Way||Link|
|EVGA||Pro SLI Bridge V2||Solid||4-Way||Link|
|GIGABYTE||3-Way SLI Bridge||Solid||3-Way||Link|
|MSI||2-WAY SLI BRIDGE L TITANIUM||Solid||2-Way||40mm||Link|
|MSI||Gaming 2-WAY SLI BRIDGE L||Solid||2-Way||40mm||Link|
|NETCNA||3-Way SLI Bridge||Solid||3-Way||Link|
|NVIDIA||2 Way Single SLI Bridge||Solid||2-Way||40mm||Link|
|NVIDIA||2-Way Spaced Bridge||Solid||2-Way||60mm||Link|
SLI Bridge X-Ray Analysis
Flexible 2-Way Bridge
Below you see pictures of the X-ray analysis of a flexible 2-way SLI bridge from ASUS. It’s a very common SLI bridge which I picked out of the box of my Rampage V Edition 10 (Amazon). A flexible bridge is variable in length and thus very useful for all kind of SLI configurations.
You can clearly see that the SLI bridge is just a plain point-to-point connection. There are no special components such as ICs, capacitors or resistors. You can also see voids inside the soldering (white spots inside the dark soldering area), but the amount is still within tolerance and won’t cause any problems or signal loss.
Solid 2-Way Bridge
The next bridge is solid comes from ASRock and is also meant for 2-way SLI. Looking at the X-Ray pictures you can also see a lot of traces and also vias which connect different PCB layers. In this case the top and bottom layer are ground (GND) and connected with the vias. The solder quality is a little bit worse than the flexible ASUS bridge but still fine to use. Technically there is no difference compared to the flexible bridge – also here no special components.
Solid 3-Way Bridge
The ASUS 3-Way SLI bridge is technically also very similar to the bridges above. Solder quality is decent and you can mainly see straight connections between the different connectors. You can see that this is clearly a multi-layer bridge with 4 PCB layers (notice: different gray shades which indicate the X-ray depth).
NVIDIA 2-Way LED Bridge
So let’s go over to the more interesting part: NVIDIA’s LED Bridge. Just by looking at the first picture you will notice that there is a slight difference compared to the other bridges. Some traces are not straight but wave-shaped. This bridge has an adjusted trace-length to make sure all traces on the bridge have exactly the same length. This will improve the signal quality for high frequency operations, which makes sense if you increase the frequency from 400 to 650 MHz.
The parts which you can see in the middle are additional ICs, resistors and capacitors which are just for the LED operation. None of these components have influence on function or performance.
In addition the solder quality is a bit better than compared to the other 3 bridges listed above. There is only a very small amount of voids inside the soldering.
EVGA 2-Way HB SLI Bridge
The EVGA HB Bridge is essentially the same as two normal NVIDIA LED bridges. The HB Bridge is also optimized for the best signal quality with adjusted traces and also with good solder quality.
The additional components on this bridge are also just for LED control and not related to the SLI performance.
SLI Bridge Electrical Analysis
From a technical point of view the new SLI bridge is not quantum leap in either electrical engineering or design. Essentially it’s the same as two “LED bridges” combined in one PCB. For sure the signal quality is better than using a old flex bridge. However it seems a bit over the top that NVIDIA claims a huge effort in development while adjusting traces to the same length is usually just one click in the development software and takes only few seconds.
Apart from the adjusted trace length all bridges look very similar and I couldn’t find any major difference. So the question is: How does the NVIDIA driver identify the HB Bridge if there is no technical difference? So I grabbed my multi-meter and tracked down the traces on the SLI bridge to see what they actually do.
Each SLI connector has 26 pins in total. However, if you count the traces on the PCB you will only find 20 traces.
I found out that 20 pins are for data transfer and 6 pins are connected to ground (GND) on the flexible legacy bridge.
The LED / HB Bridge is slightly different. One pin is not routed to ground but no supplies 1.8 Volt to the SLI Bridge. This supply voltage is also used to feed the LED. In addition the driver can notice if the pin is bridge to ground or not. Bridged to ground, the driver detects a legacy bridge. Not bridged to ground it will detect a HB bridge.
Knowing that there is no difference apart from the tracing I didn’t really expect too much. Even though I already read other reviews online I still wanted to test the performance myself.
NVIDIA SLI Bridge Performance Test
I tested the new HB Bridge vs 1 LED Bridge vs 1 and 2 flexible legacy bridges. I know you don’t love synthetic benchmarks such as Fire Strike so I also tested Crysis 3, Far Cry Primal and Rainbow Six Siege. I ran all games with 4K resolution and the highest settings available.
- Intel Core i7-6950X @ 4.0 GHz ((Find at Amazon)
- ASUS ROG Rampage 5 Edition 10 (Find at Amazon)
- 4x 8 GB DDR4-3000 C16
- Noctua NH-D15 (Find at Amazon)
- 2x NVIDIA GeForce GTX 1080 Founders Edition (Find at Amazon)
- Corsair AX1200i Power Supply (Find at Amazon)
- Windows 10 x64
- ASUS PB287Q 4K Monitor (Find at Amazon)
NVIDIA SLI Bridge Test Results
The results are rather disillusioning. 3DMark Fire Strike Extreme benefits a bit and gains about 200 points going from legacy to a new bridge. Crysis 3 doesn’t scale at all, Far Cry Primal about 1 FPS and Rainbow Six Siege gains about 3-4 FPS which is an increase of roughly 5 %. Overall I could see no difference between the LED bridge and the new HB bridge.
NVIDIA HB SLI Bridge: Conclusion
Yay or nay? Neither of both I’d say. The NVIDIA HB SLI Bridge is slightly better than the legacy bridges but the difference is very small. It seems like you can gain few extra FPS in some games and it’s also likely that the new bridge will improve the gaming experience overall by reducing the micro-stuttering. Is the bridge worth USD $45? I’d say no, but taking into account how much you have to pay for two GeForce GTX 1080 graphics cards, chucking out another 45 dollar isn’t going to make the difference.
If you plan to get a multi-GPU system you might as well get the new High Bandwidth SLI bridge, but don’t expect a huge performance difference. If you already own a LED bridge, there is no point in upgrading apart from bragging rights.
Are you using the High Bandwidth bridges? Let me know your thoughts on this topic below. Thanks for reading and until the next one!